Valid Markup saves battery life
T-Mobile in their position paper to the Mobile Web Initiative Workshop note that
The very fact that advanced browsers allow greater mark-up flexibility unfortunately reduced the amount of care taken to assure standards compliance and led to a broader use of sloppy mark-up – but unlike to desktop browsing this has quite severe consequences for users of devices with radically limited resources: rendering non-deterministic mark-up has a very real impact on CPU, memory and battery life, and also mostly leads to unwanted and costly data overhead on the radio transmission – for customers and operators all alike.